The present invention is related to gaskets and particularly to gaskets used in hose couplings that connect the air lines between railway cars.
Railway cars employ air brakes which require a brake pipe on each car via which pneumatic control signals may be transmitted to the respective cars when the brake pipes of adjacent cars are interconnected to form a continuous train line. Due to relative movement between the cars, a flexible hose is attached to the brake pipe at each end of the car having special couplings that join the hoses together to form the continuous train line. These hose couplings are fitted with gaskets that mate and seal with the gasket of an adjoining coupling to effect a substantially leak free connection, which is essential for proper control of the train air brakes, particularly on long trains where even minimal leakage at the numerous couplings can cause such a pressure gradient, from the front to the rear of the train, as to be intolerable.
Similar hoses and hose couplings are also provided on the various air lines on locomotives to permit coupling of these air lines between locomotives in a train-consist. Leakage at the hose couplings has been attributed primarily to mis-alignment between the gasket and the gasket retaining groove of the hose coupling. Several factors are known to influence gasket mis-alignment including torque distortion during coupling, cold temperature shrinkage of the gasket, and dimensional variations of the gasket retaining groove.
The present standard gasket approved by the A.A.R. (American Association of Railroads) is an annular, one-piece body having a radially extending, annular retaining flange that is adapted to be forced or pressed into the retaining groove of a conventional hose coupling head and an axially extending annular face portion that projects beyond the mouth of the hose coupling head and is adapted to engage the corresponding part of a companion hose coupling gasket to effect a seal therebetween. An annular, axial opening is provided in the gasket to accommodate the passage of air. On one side of the gasket retaining flange, there is formed a sealing bead that is situated in substantially axially opposed alignment with the gasket sealing face to obtain a "column" loading when the gasket is under compression during coupling, the purpose being to achieve a positive seal between the gasket and the gasket retaining groove formed in the hose coupling head. In so situating this sealing bead, however, the sealing bead lies at the very edge of the gasket retaining groove. Consequently, only slight mis-alignment between the gasket and retaining groove can cause the gasket sealing bead to become displaced relative to its intended point of engagement with the gasket retaining groove in the coupler head. Such a consequence, of course, results in loss of the gasket seal with the hose coupling head at the sealing bead, so that air is able to leak from the coupling air passage around the gasket flange and escape to atmosphere. It will be appreciated, therefore, that even though the integrity of the pressure seal is maintained at the mating faces of the adjoining hose coupling gaskets, a major source of leakage can occur via the gasket retaining groove.